Sheet conveying device, image forming apparatus, and sheet conveying method

ABSTRACT

According to one embodiment, a sheet conveying device includes a paper feeding roller, a separating roller, a double-feed detection section, a double-feed determining section, a torque limiter, a driving section, and a driving force-input control section. The paper feeding roller conveys a sheet. The separating roller separates sheets doubly fed to a nip between the separating roller and the paper feeding roller. The double-feed detection section detects conveyance state of the sheets to the nip and outputs a detection signal. The double-feed determining section determines, on the basis of the detection signal, whether sheets conveyed to the nip are doubly fed. If only one sheet is conveyed to the nip, the torque limiter allows the separating roller to be driven to rotate following the paper feeding roller. The driving section inputs driving force to the separating roller via the torque limiter. If the double-feed determining section determines that the sheets are doubly fed, the driving force-input control section causes the driving section to input the driving force to the torque limiter and, if the double-feed determining section determines that the sheets are not doubly fed, the driving force-input control section stops the input of the driving force to the torque limiter by the driving section.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from U.S. provisional application 61/332,698, filed on May 7, 2010; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a technique for stably conveying sheets while preventing double feed.

BACKGROUND

FIG. 6 is a perspective view of a sheet conveying device 3A of an image forming apparatus in the past.

A sheet picked up from a tray by a pickup roller 31 is conveyed to a nip N between a paper feeding roller 32 and a separating roller 33. Driving force T1 is transmitted from a shaft 331 to the separating roller 33 in a return direction (a counterclockwise direction in FIG. 6) via a torque limiter 34A. If only one sheet goes into the nip N, as shown in FIG. 7, driving force T2 is transmitted from the paper feeding roller 32 to the separating roller 33 via the sheet. The driving force T2 transmitted from the separating roller 33 to the torque limiter 34A is a load equal to or larger than a set value. Consequently, a slip occurs in the torque limiter 34A. Although the separating roller 33 receives driving force T1A in the return direction from the torque limiter 34A, the separating roller 33 is driven to rotate following the paper feeding roller 32 in a feeding direction (a clockwise direction in FIG. 7) by the driving force T2 transmitted from the paper feeding roller 32.

On the other hand, if more than two sheets go into the nip N, as shown in FIG. 8, since a friction coefficient among the sheets is low, driving force T3 enough for not causing a slip in the torque limiter 34A is transmitted from the paper feeding roller 32 to the separating roller 33. Therefore, the separating roller 33 rotates in the return direction with the driving force T1 input from the shaft 331. Therefore, if more than two sheets go into the nip N, conveyance of the sheet at the bottom in contact with the separating roller 33 is stopped by the separating roller 33 and the sheet at the top in contact with the paper feeding roller 32 is conveyed by the paper feeding roller 32.

However, in the sheet conveying device in the past, even during normal conveyance when only one sheet goes into the nip N, the torque limiter 34A transmits the driving force T1A in the return direction to the separating roller 33. Therefore, the conveyance of the sheet tends to be unstable and it is likely that a skew, a conveyance delay, and partial wear of the separating roller 33 occur.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the configuration of an image forming apparatus;

FIG. 2 is a perspective view of a sheet conveying device;

FIG. 3 is an enlarged side view of a double-feed detection sensor;

FIG. 4 is a block diagram of functional sections realized by a control section;

FIG. 5 is a flowchart for explaining sheet conveyance processing;

FIG. 6 is a perspective view of a sheet conveying device of an image forming apparatus in the past;

FIG. 7 is a schematic diagram for explaining an action of a separating roller during normal conveyance; and

FIG. 8 is a schematic diagram for explaining an action of the separating roller during double feed.

DETAILED DESCRIPTION

According to one embodiment, a sheet conveying device includes a paper feeding roller, a separating roller, a double-feed detection section, a double-feed determining section, a torque limiter, a driving section, and a driving force-input control section. The paper feeding roller conveys a sheet. The separating roller separates sheets doubly fed to a nip between the separating roller and the paper feeding roller. The double-feed detection section detects conveyance state of the sheets to the nip and outputs a detection signal. The double-feed determining section determines, on the basis of the detection signal, whether sheets conveyed to the nip are doubly fed. If only one sheet is conveyed to the nip, the torque limiter allows the separating roller to be driven to rotate following the paper feeding roller. The driving section inputs driving force to the separating roller via the torque limiter. If the double-feed determining section determines that the sheets are doubly fed, the driving force-input control section causes the driving section to input the driving force to the torque limiter and, if the double-feed determining section determines that the sheets are not doubly fed, the driving force-input control section stops the input of the driving force to the torque limiter by the driving section.

In general, according to another embodiment, a sheet conveying method by an image forming apparatus including: a paper feeding roller configured to convey a sheet; a separating roller configured to separate sheets doubly fed to a nip between the separating roller and the paper feeding roller; a double-feed detection section configured to detect conveyance state of sheets to the nip and output a detection signal; a torque limiter configured to allow, if only one sheet is conveyed to the nip, the separating roller to be driven to rotate following the paper feeding roller; and a driving section configured to input driving force to the separating roller via the torque limiter.

The sheet conveying method includes: determining, on the basis of the detection signal, whether sheets conveyed to the nip are doubly fed; and

causing, if it is determined that the sheets are doubly fed, the driving section to input the driving force to the torque limiter and stopping, if it is determined that the sheets are not doubly fed, the input of the driving force to the torque limiter by the driving section. An embodiment is explained below with reference to the drawings.

FIG. 1 is a diagram of the configuration of an image forming apparatus 1. In FIG. 1, an upward direction is represented as Z direction, a right direction is represented as X direction, and a vertical direction on paper surface is represented as Y direction.

The image forming apparatus 1 is a MFP (Multi Function Peripheral). The image forming apparatus 1 includes a control section 2, a display section 11, an image reading section 12, a sheet feeding section 13, and an image forming section 14. The control section 2 includes a processor 21, a memory 22, a HDD (Hard Disk Drive) 23, and an ASIC (Application Specific Integrated Circuit) 24 and controls the entire image forming apparatus 1. The display section 11 includes an operation input section 111 configured to receive an operation input. The display section 11 displays, for example, setting of the image forming apparatus 1 and receives the operation input. The image reading section 12 is an ADF (Auto Document Feeder) and reads an original document. The sheet feeding section 13 includes plural paper feeding cassettes 131 configured to store sheets, a conveying path 132 for conveying a sheet picked up from the paper feeding cassettes 131 to the image forming section 14, and a sheet conveying device 3 configured to pick up the sheets from the paper feeding cassettes 131 one by one and convey the sheet to the conveying path 132. The conveying path 132 is a part of the sheet conveying device 3.

Driving force from a driving system 134 including a conveying path driving motor 133 is transmitted to conveying rollers of the conveying path 132. The image forming section 14 includes a transfer belt 141 configured to transfer a toner image onto the sheet conveyed from the sheet feeding section 13 and a fixing device 142 configured to heat and press the sheet and fix the toner image on the sheet.

FIG. 2 is a perspective view of the sheet conveying device 3.

The sheet conveying device 3 includes the conveying path 132, a pickup roller 31, a paper feeding roller 32, a separating roller 33, a torque limiter incorporating gear 34 (a torque limiter), an electromagnetic clutch 35, a gear 36 (a driving force input section and a torque transmitting section), and a double-feed detection sensor 37 (a double-feed detection section, FIG. 3), and a sensor for feeding paper 39 (FIG. 3).

The pickup roller 31 picks up the sheets from the paper feeding cassette 131 one by one.

The paper feeding roller 32 conveys the sheet to the conveying path 132. Pickup roller 31 is driven by the paper feeding roller 32 via the gear.

The separating roller 33 comes into press contact with the paper feeding roller 32. A press contact area between the separating roller 33 and the paper feeding roller 32 is referred to as nip N. The separating roller 33 separates sheets which are more than two pieces and which go into the nip N. The separating roller 33 is provided at one end of the shaft 331. A gear 332 is provided at the other end of the shaft 311.

The torque limiter incorporating gear 34 incorporates a torque limiter. A gear provided on the outer circumference of the torque limiter incorporating gear 34 meshes with the gear 332 provided in the shaft 331 of the separating roller 33. The torque limiter incorporating gear 34 is provided at one end of a shaft 341. The electromagnetic clutch 35 is provided at the other end of the shaft 341.

The gear 36 is couple with driving system 134 configured to drive the conveying rollers of the conveying path 132 and transmits the driving force to the electromagnetic clutch 35, the driving force which tries to drive the separating roller 33 in a return direction which is opposite direction to a direction for conveying sheet.

The electromagnetic clutch 35 is provided between the gear 36 and the torque limiter incorporating gear 34. Under the control by the control section 2, during the normal conveyance, the electromagnetic clutch 35 is turned off and disconnects transmission of driving force from the gear 36 to the torque limiter incorporating gear 34. Under the control by the control section 2, during double feed, the electromagnetic clutch 35 is turned on and connects the transmission of driving force from the gear 36 to the torque limiter incorporating gear 34. A driving section 38 includes the electromagnetic clutch 35, the gear 36, and the shaft 341. The driving section 38 inputs driving force to the separating roller 33 via the torque limiter incorporating gear 34.

FIG. 3 is an enlarged side view of the double-feed detection sensor 37.

The double-feed detection sensor 37 detects double feed of sheets. The double-feed detection sensor 37 includes an actuator 371 and a magnetic resistance sensor. A part of the actuator 371 is exposed to downstream in a sheet conveying direction of the nip N in the conveying path 132 and is capable of turning. In the conveying path 132, a projecting section 135 that projects from a wall surface of the conveying path 132 and is opposed to the actuator 371 is provided downstream in the sheet conveying direction of the nip N. The actuator 371 comes into press contact with the projecting section 135.

The magnetic resistance sensor is provided on the inside of the double feed sensor 37 and changes an output voltage according to a variation of the actuator 371. When the actuator 371 is turned by a sheet going into a space between the projecting section 135 and the actuator 371 passing through the nip N, the output voltage of the magnetic resistance sensor fluctuates. Consequently, the double-feed detection sensor 37 detects sheet thickness double feed and outputs a voltage (a detection signal) to the control section 2. The control section 2 compares the voltage output by the double-feed detection sensor 37 with a voltage (threshold) output by the double-feed detection sensor 37 when one sheet goes into a nip N, and determines whether sheet going into the nip N is one piece or more than two pieces. In this embodiment, the double-feed detection sensor 37 is a contact type sensor that detects double feed according to a variation of the actuator 371. However, the double-feed detection sensor may be a non-contact type sensor. For example, the double-feed detection sensor may be a light-transmission type sensor that emits light to a sheet passing through the conveying path 132, receives light transmitted through the sheet, and detects double feed according to a state of blocking of the light by the sheet.

The sensor for feeding paper 39, for example the light-transmission type sensor, detects that sheet passes the paper feeding roller 32.

FIG. 4 is a block diagram of functional sections realized by the control section 2.

The image forming apparatus 1 includes a double-feed determining section 41 and a driving force-input control section 42 as functional sections realized by the processor 21 reading a computer program stored in the memory 22 or the HDD 23. The sections 41 and 42 are components of the sheet conveying device 3 as well. The ASIC 24 may realize functions of the sections 41 and 42.

Sheet conveyance processing by the sheet conveying device 3 in conveying sheets picked up by the pickup roller 31 to the conveying path 132 one by one is explained with reference to a flowchart of FIG. 5. The sheet conveyance processing is realized by the processor 21 reading the computer program stored in the memory 22 or the HDD 23.

First, the control section 2 picks up a sheet from the paper feeding cassette 131 using the pickup roller 31 and conveys the sheet to the nip N between the paper feeding roller 32 and the separating roller 33.

Subsequently, the paper feeding roller 32 conveys the sheet going into the nip N in the sheet conveying direction (ACT 1). In ACT 1, the electromagnetic clutch 35 is off, therefore the shaft 341 runs idle on the shaft of the electromagnetic clutch 35 and the driving forth from the driving system 134 is transmitted to the separating roller 33. Subsequently, the separating roller 33 is in an idling state and driven to rotate following the paper feeding roller 32. In ACT 2 to ACT 6 explained below, the control section 2 continues to drive the paper feeding roller 32 and the pickup roller 31.

As shown in FIG. 3, when a sheet is slightly conveyed in the sheet conveying direction by the paper feeding roller 32 and the separating roller 33 while being held between the paper feeding roller 32 and the separating roller 33, the sheet comes into contact with the actuator 371 and the double-feed detection sensor 37 outputs a voltage corresponding to sheet thickness to the control section 2.

The double-feed determining section 41 determines, on the basis of the voltage output by the double-feed detection sensor 37, whether sheet going into the nip N is one piece or more than two pieces (ACT 2).

If the double-feed determining section 41 determines that the sheets go into the nip N (YES in ACT 2), the driving force-input control section 42 turns on the electromagnetic clutch 35 and transmits the driving force from the driving system 134 to the separating roller 33 via the gear 36 (ACT 3). Consequently, the separating roller 33 is transmitted driving force via the torque limiter incorporating gear 34. The separating roller 33 rotates in the return direction. Therefore, the conveyance of the sheet at the bottom among the sheets going into the nip N more than two pieces is stopped. Only one sheet at the top is conveyed in order in the sheet conveying direction by the paper feeding roller 32 (see FIG. 8).

If only one sheet remains held between the paper feeding roller 32 and the separating roller 33, the double-feed determining section 41 determines, on the basis of the voltage output by the double-feed detection sensor 37, that one sheet goes into the nip N (NO in ACT 2). Then, if the electromagnetic clutch 35 is ON (YES in ACT 4), the driving force-input control section 42 turns off the electromagnetic clutch 35 and disconnects the transmission of driving force from the gear 36 to the torque limiter incorporating gear 34 (ACT 5). Consequently, the separating roller 33 idles and is driven to rotate following the paper feeding roller 32. The sheet is conveyed in the sheet conveying direction by the paper feeding roller 32 and the separating roller 33 that is driven to rotate following the paper feeding roller 32.

If the control section 2 determines that predetermined sheets necessary for the image forming apparatus to process a job were conveyed after predetermined time goes on since the timing of starting to extract sheet and convey sheet with paper feeding roller 32 (YES in ACT6), the control section 2 disable the paper feeding roller 32 extracting sheet and the pickup roller 31 conveying sheet (ACT7). Furthermore, the control section 2 can detect number of sheet conveyed on the basis of signal from the sensor for feeding sheet 39.

In this embodiment, during the normal conveyance when only one sheet goes into the nip N, the torque limiter incorporating gear 34 does not transmit driving force in the return direction to the separating roller 33. Therefore, it is possible to stably convey sheets and prevent occurrence of a skew, a conveyance delay, and partial wear of the separating roller.

As a comparative example in which a configuration for not transmitting driving force in the return direction to the separating roller 33 during the normal conveyance is adopted, a sheet conveying device is considered in which a motor is directly connected to the separating roller, the separating roller is rotated in the return direction during more than two sheets go into the nip N, and the separating roller is rotated in the feeding direction during the normal conveyance that one sheet goes into the nip N.

In the comparative example, a physical time lag, for example the slowdown time and acceleration time for motor and back rush of the gear, occurs after it is detected that a double-feed state is switched to a normal conveyance state until a driving direction of the motor is changed and actually switched. Therefore, in the comparative example, even after it is detected that the double-feed state is switched to the normal conveyance state, during the time lag, the separating roller 33 rotates in the return direction in a state in which the paper feeding roller 32 is rotating in the feeding direction. Consequently, an impossible load occurs to a sheet and that causes conveyance badness.

Compared with the comparative example, in this embodiment, in the double-feed state, the separating roller 33 is driven via the torque limiter incorporating gear 34. Therefore, in this embodiment, during a time lag after it is detected that the double-feed state is switched to the normal conveyance state until the electromagnetic clutch 35 is actually switched from ON to OFF, a state same as the state in the past shown in FIG. 7 occurs. Specifically, in this embodiment, during the time lag until the electromagnetic clutch 35 is switched from ON to OFF, driving force in the return direction is transmitted to the separating roller 33 via the torque limiter incorporating gear 34. However, the separating roller 33 is driven to rotate following the paper feeding roller 32 according to the transmission of the driving force from the paper feeding roller 32. Therefore, in this embodiment, it is possible to prevent a sheet from being impossible load. In this embodiment, since the driving force in the return direction is transmitted to the separating roller 33 only during the time lag, during the normal conveyance, it is possible to suppress the adverse effect due to the transmission of the driving force in the return direction to the separating roller 33.

As explained in detail, according to the technique described in this specification, it is possible to provide a technique for stably conveying sheets while preventing double feed.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus, methods and system described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus, methods and system described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

1. A sheet conveying device comprising: a paper feeding roller configured to convey a sheet; a separating roller configured to separate sheets doubly fed to a nip between the separating roller and the paper feeding roller; a double-feed detection section configured to detect conveyance state of the sheets to the nip and output a detection signal; a double-feed determining section configured to determine, on the basis of the detection signal, whether sheets conveyed to the nip are doubly fed; a torque limiter configured to allow, if only one sheet is conveyed to the nip, the separating roller to be driven to rotate following the paper feeding roller; a driving section configured to input driving force to the separating roller via the torque limiter; and a driving force-input control section configured to cause, if the double-feed determining section determines that the sheets are doubly fed, the driving section to input the driving force to the torque limiter and stop, if the double-feed determining section determines that the sheets are not doubly fed, the input of the driving force to the torque limiter by the driving section.
 2. The device according to claim 1, wherein the driving section includes: a driving force input section configured to input driving force to the torque limiter; and a clutch provided between the driving force input section and the torque limiter and configured to connect or disconnect transmission of driving force from the driving force input section to the torque limiter under control by the driving force-input control section.
 3. The device according to claim 2, wherein the torque limiter and the clutch are provided on a same shaft, and the shaft is different from a shaft of the separating roller.
 4. The device according to claim 2, further comprising: a conveying roller configured to convey the sheet that finishes passing through the nip in the sheet conveying direction; a driving system configured to drive the conveying roller; and a transmitting section configured to transmit the driving force from the driving system to the clutch.
 5. The device according to claim 1, wherein a point of detection by the double-feed detection section is further downstream in a sheet conveying direction than the nip.
 6. The device according to claim 1, wherein the driving section inputs, to the separating roller, driving force in a direction opposite to a direction of the driven rotation.
 7. An image forming apparatus comprising: a paper feeding roller configured to convey a sheet; a separating roller configured to separate sheets doubly fed to a nip between the separating roller and the paper feeding roller; a double-feed detection section configured to detect conveyance state of the sheets to the nip and output a detection signal; a double-feed determining section configured to determine, on the basis of the detection signal, whether sheets conveyed to the nip are doubly fed; a torque limiter configured to allow, if only one sheet is conveyed to the nip, the separating roller to be driven to rotate following the paper feeding roller; a driving section configured to input driving force to the separating roller via the torque limiter; a driving force-input control section configured to cause, if the double-feed determining section determines that the sheets are doubly fed, the driving section to input the driving force to the torque limiter and stop, if the double-feed determining section determines that the sheets are not doubly fed, the input of the driving force to the torque limiter by the driving section; and an image forming section configured to form an image on a sheet that finishes passing through the nip.
 8. The apparatus according to claim 7, wherein the driving section includes: a driving force input section configured to input driving force to the torque limiter; and a clutch provided between the driving force input section and the torque limiter and configured to connect or disconnect transmission of driving force from the driving force input section to the torque limiter under control by the driving force-input control section.
 9. The apparatus according to claim 8, further comprising: a conveying roller configured to convey the sheet that finishes passing through the nip to the image forming section side; a driving system configured to drive the conveying roller; and a transmitting section configured to transmit the driving force from the driving system to the clutch.
 10. The apparatus according to claim 8, wherein the torque limiter and the clutch are provided on a same shaft, and the shaft is different from a shaft of the separating roller.
 11. The apparatus according to claim 10, wherein the torque limiter is integral with a gear which meshes with a gear provided in the shaft of the separating roller.
 12. The apparatus according to claim 7, wherein a point of detection by the double-feed detection section is further downstream in a sheet conveying direction than the nip.
 13. The apparatus according to claim 7, wherein the driving section inputs, to the separating roller, driving force in a direction opposite to a direction of the driven rotation.
 14. A sheet conveying method by an image forming apparatus including: a paper feeding roller configured to convey a sheet; a separating roller configured to separate sheets doubly fed to a nip between the separating roller and the paper feeding roller; a double-feed detection section configured to detect conveyance state of sheets to the nip and output a detection signal; a torque limiter configured to allow, if only one sheet is conveyed to the nip, the separating roller to be driven to rotate following the paper feeding roller; and a driving section configured to input driving force to the separating roller via the torque limiter, the sheet conveying method comprising: determining, on the basis of the detection signal, whether sheets conveyed to the nip are doubly fed; and causing, if it is determined that the sheets are doubly fed, the driving section to input the driving force to the torque limiter and stopping, if it is determined that the sheets are not doubly fed, the input of the driving force to the torque limiter by the driving section.
 15. The method according to claim 14, wherein the driving section includes: a driving force input section configured to input driving force to the torque limiter; and a clutch provided between the driving force input section and the torque limiter and configured to connect or disconnect transmission of driving force from the driving force input section to the torque limiter, and the method further comprises connecting or disconnecting the clutch on the basis of a result of determination concerning whether sheets are doubly fed.
 16. The method according to claim 15, wherein the image forming apparatus further includes: a conveying roller configured to convey a sheet that finishes passing through the nip to an image forming section side; a driving system configured to drive the conveying roller; and a transmitting section configured to transmit the driving force from the driving system to the clutch.
 17. The method according to claim 15, wherein the torque limiter and the clutch are provided on a same shaft, and the shaft is different from a shaft of the separating roller.
 18. The method according to claim 17, wherein the torque limiter is integral with a gear which meshes with a gear provided in the shaft of the separating roller.
 19. The method according to claim 14, wherein a point of detection by the double-feed detection section is further downstream in a sheet conveying direction than the nip.
 20. The method according to claim 14, wherein the driving section inputs, to the separating roller, driving force in a direction opposite to a direction of the driven rotation. 